Yes, those requirements are too restrictive.
Or at least, they aren't helpful requirements.
So, Cort Ammon mentioned the generation gap. Your 18-year olds will be 40 before other 18-year olds will be old enough to fill the gap in the workforce, which is tricky but doable. Your fifty year olds will be one hundred before the next generation reaches fifty, which is much less doable. Your young 18-year olds will be at most thirty when the last of the first generation is over fifty (assuming that's a cutoff for a reason), and either there will not be enough to do all the work (because the younger kids are still aging into workforce-age), or you have too many people because there are enough workers but kids (their own replacements) are extra. You need to have replacements ready when someone retires, or dies, or can't do whatever work is needed because of injury or illness - and replacements that take twenty years to arrive are not ideal.
Your first generation must keep working at the same efficiency with no retirement or replacement (while reproducing and raising enough kids to completely replace themselves) for at least twenty years, and even then replacement will be slow, since a generation ship has to control reproduction to not overgrow their resources. Your next generation may be packed into ten years (so as to not have a situation where there aren't enough workers), which can lead to too big a population overlap since they have to reproduce to replace themselves, too. Slow careful reproduction is much more sustainable than this kind of rigid generation gap.
More reasonably, you should plan that kids (and post-retirement elders) will be "extras" - kids not included into the workforce until survival training at eighteen, elders easing off on duties as they can't keep up the level of work. It will let your population adapt to a slow aging in and out of various categories, instead of large overlaps and gaps that will take generations to balance out.
Also, your aliens have some odd prejudices. Restricting overweight and underweight, well, there are some points (especially dealing with medical problems) but it's oddly done - especially without a discussion of what qualifies and how. Varied body types should probably be included in your diversity, especially since the destination environment isn't known. I can understand wanting healthy versions of said body types, just, that is a different requirement than not "underweight" or not "overweight/obese" - especially since mildly overweight is actually a touch healthier than normal weight (because it is aesthetically rather than medically determined), and usual measurements (like the BMI) are notoriously inaccurate.
Also, you mentioned survival training - and the body types that hold on to weight have some actual survival benefit, as a backup energy source and a buffer against lean times or stresses like illness. The tradeoffs of this benefit cause problems in places where overabundance, rather than scarcity, is a problem - but given survival training and an uncertain destination, losing this benefit without discussion may not serve. It may be better to restrict by healthy bodies or active lifestyles (trickier to control for, but better results), rather than policing weight or shape. Restricting by active lifestyle or healthy bodies will also likely leave far fewer people than just restricting to "normal-weight" people, but they will probably be better candidates anyway.
The restriction on orphans is just odd, really - especially since it would necessarily make all your candidates more reluctant to go, knowing they're leaving their families behind! It may disproportionately affect the older demographics on your list, since their parents will be lost to age as well as tragedy. In truth, it might make sense to prefer orphans and/or those without strong familial ties, so that they will have less to regret leaving behind. I could also understand not wanting any children on board to be orphans (in case you relax that restriction), if you're assuming that their parents are on board with them.
As for severe illness and other chronic health conditions, it does make sense to restrict them - especially since it may eliminate some of these conditions in your population. Even restricting those who are actually ill with minor illness might help, since you may prevent those diseases from getting on the ship at all - no guarantees, but it's possible.
And, you should probably consider a few more restrictions - simple things like passing a background check - so not having a criminal record, you probably don't want mass-murderers or serial killers on your ship.
You should prefer people having a good work ethic, and prioritize those having useful knowledge and experience, possibly making an education restriction. You can focus on technical fields (scientists and such), or else craftspeople and artisans, or even survival skills (hey, you're testing for it - might as well screen for it first!)... it depends on the conditions expected on board the ship, what kinds of work will need to be done while the ship is voyaging, and what kinds of conditions are anticipated on the other end of the trip. Knowledge and skills can only be passed down if they made it on the ship to begin with!
You should probably add a requirement for metal health, to go with your requirements for physical health. You should also keep an eye on personality and interpersonal skills, since with such a small population and a long voyage, there will be plenty of room for friction and no where to go to escape people when conflicts happen and drama is everywhere. Much better to minimize that when you can. This may also alleviate some of your concerns about teens not being mature yet - in the beginning, you can select for those that are, at least, better.
You will likely also want to select for those with compatible philosophies, social or political leanings, or whatever equivalents your aliens are going with - so that the population will (hopefully) grow the society they wanted to see in the first place. This would likely be done in the last stage, handpicking from your remaining possibilities, but it probably should be mentioned anyway.